RFID is a data collection technology that uses radio-sensitive tags for storing data. RFID tags, which are also commonly referred to as transponders, typically comprise two parts. The first part is an integrated circuit for storing and processing data, modulating and demodulating RF signals, and performing other specialized functions. The second part is an antenna that provides the means for the integrated circuit to transmit its stored data to an RFID reading device. An RFID reading device is also called an interrogator.
The communications between an RFID tag and an RFID reading device take place over a radio-based air interface. One such air interface is the Gen 2 air interface, which is a standard administered by EPCglobal Inc. Gen 2 defines, among other things, requirements for the format of the data, such as an Electronic Product Code (EPC), stored in the integrated circuit of an RFID tag. According to Gen 2, an EPC must comprise at least ninety-six bits and can include a unique serial number of a particular product to which a Gen 2 RFID tag is attached.
FIG. 1 is an illustration of an exemplary EPC 100. EPC 100 comprises header 102, manager number 104, object class 106, and serial number 108. Header 102 is eight bits in size, manager number 104 is twenty-eight bits in size, object class 106 is twenty-four bits in size, and serial number 108 is thirty-six bits in size. While EPC 700 is ninety-six bits in size, other EPCs can have different sizes that can be defined by EPCglobal Inc., e.g., sixty-four bits. Each two digit sequence in EPC 100 is a hexadecimal number representing eight bits (one byte) of EPC 100. Header 102 defines the length, type, structure version, and generation of EPC 100 (e.g., Gen 2). Manager number 104 is the entity responsible for maintaining object class 106 and serial number 108, e.g., a manufacturer. Object class 106 identifies a product. Object class 106 can be, e.g., a stock keeping unit (SKU) or consumer unit. Serial number 108 identifies a unique serial number for the product within object class 106. Thus, while object class 106 can categorically identify, e.g., a type of cereal product, serial number 108 can identify a particular box of the type of cereal product identified by object class 106.
In contrast to EPCs, Universal Product Codes (UPCs) and European (International) Article Numbers (EANs), which are typically encoded in bar codes, are devoid of a unique serial number having the purpose of serial number 108. Instead, UPCs and EANs have manufacturer codes analogous to manager number 104 and product codes analogous to object class 106, and are therefore more limited to categorically identifying, e.g., a type of cereal product of a manufacturer. UPCs and EANs can have different formats. For example, UPCs can be in UPC-A or UPC-E format, and EANs can be in EAN-13 or EAN-8 format.
FIG. 2 is an illustration of an exemplary twelve-digit UPC-A bar code 200. UPC-A bar code 200 comprises number system character 202, manufacturer code 204, product code 206, and check digit 208. Number system character 202 characterizes specific types of bar codes and appears on the left of bar code 200. Number system character 202 can be “0”, which is a standard UPC number code, “1”, which is a reserved code, “2”, which is a code for random weight items like fruits, vegetables, and meats, “3”, which is a code for pharmaceuticals, “4”, which is an in-store code for retailers, “5”, which is a code for coupons, “6”, which is a standard UPC number code, “7”, which is a standard UPC number code, “8”, which is a reserved code, or “9”, which is a reserved code. Manufacturer code 204 is a five digit number specifically assigned to the manufacturer of the product bearing bar code 200. Manufacturer codes are maintained and assigned by the Uniform Code Council (UCC). Each product of a manufacturer carries the same manufacturer code. For example, the manufacturer code for all Kellogg's® products is 38000. Kellogg's is a trademark or registered trademark of Kellogg NA Co. in the United States, other countries, or both. Product code 206 is a five digit number that the manufacturer assigns for a particular product. Each different product and each different packaging or size is assigned a unique product code. For example, while the product code for Kellogg's® 13.5 oz. Rice Krispies® is 90530, the product code for Kellogg's® 16 oz. Mini-Wheats® is 02720. Rice Krispies and Mini-Wheats are trademarks or registered trademarks of Kellogg NA Co. in the United States, other countries, or both. A manufacturer can have up to 99,999 unique product codes. Check digit 208 is located on the outside right of bar code 200 and can be calculated using any known check digit calculation algorithm. A bar code reading device utilizes check digit 208 to validate that number system character 202, manufacturer code 210, and product code 212 were read correctly.
FIG. 3 is an illustration of an exemplary UPC-E bar code 300. UPC-E bar code 300 comprises number system character 302, which is the same as number system character 202 of UPC-A bar code 200, compressed code 304, and check digit 306, which is the same as check digit 208 of UPC-A bar code 200. Compressed code 304 is a six-digit representation of manufacturer code 204 and product code 206 of UPC-A bar code 200. Compressed code 304 can be calculated using any known UPC-A to UPC-E conversion algorithm.
FIG. 4 is an illustration of an exemplary EAN-13 bar code 400. EAN-13 bar code comprises number system 402, manufacturer code 404, product code 406, and check digit 408. Number system 402 comprises two digits that identify a country/region numbering authority. Manufacturer code 404 is a unique code assigned to each manufacturer by the numbering authority indicated in number system 402. All products of the manufacturer identified by manufacturer code 404 have an EAN-13 bar code comprising manufacturer code 404. Product code 406 is a unique code assigned by the manufacturer identified by manufacturer code 404. The total length of manufacturer code 404 and product code 406 must be ten digits. Typically, manufacturer code 404 and product code 406 are each five digits, and therefore each manufacturer can have up to 99,999 product codes. However, if a manufacturer knows that it is only going to produce a few products, a longer manufacturer code may be assigned to the manufacturer, leaving less space for the product code, and resulting in more efficient use of available manufacturer codes.
FIG. 5 is an illustration of an exemplary EAN-8 bar code 500. EAN-8 bar code 500 comprises a seven-digit message 502 and a check digit 504. The first two or three digits of message 502 identify the numbering authority, and the remaining four or five digits of message 502 identify the product. While EAN-8 is a short version of EAN-13, there are no defined methods of conversion between EAN-13 and EAN-8.
While a bar code, such as UPC-A bar code 200, UPC-E bar code 300, EAN-13 bar code 400, or EAN-8 bar code 500, must be in the line-of-sight of a bar code reading device for reading, an RFID tag need not be in the line-of-sight of an RFID reading device for reading. An RFID reading device has a radio transceiver, which generates a weak radio signal, and an antenna that transmits the radio signal. The radio signal may have a range from a few feet to a few yards. If an RFID tag receiving the radio signal is “passive,” the radio signal “wakes up” or activates the RFID tag, and the RFID tag responds by transmitting the data stored in its integrated circuit via radio signal to the RFID reading device. If the RFID tag is “active,” the RFID reading device's radio signal need not “awaken” the RFID tag. An active RFID tag has a battery that is used to boost its effective operating range. An active RFID tag will simply send its stored data by radio signal to the RFID reading device in response to receiving a radio signal from the RFID reading device. A measurement of the quality of a radio signal, e.g., a radio signal sent by an RFID tag to an RFID reading device, is a received signal strength indication (RSSI).